DCO plugin trusted_apps config not working

[clubanderson]

Description

The trusted_apps configuration option for the DCO plugin doesn't appear to work. Despite correct configuration, the DCO plugin still fails commits from trusted apps.

Environment

• Prow version: v20260109-e821f0db6
• Config synced and verified in configmap

Configuration

dco:
  org/repo:
    trusted_apps:
      - Copilot

Expected Behavior

PRs authored by GitHub Copilot (app/copilot-swe-agent) with commits from Copilot should pass DCO check automatically, as documented.

Actual Behavior

DCO check fails with "Commits in PR missing Signed-off-by" even though:

• Config is correctly synced to the plugins configmap
• Commit author login is Copilot (verified via GitHub API)
• Hook pods were restarted multiple times

Steps to Reproduce

1. Configure trusted_apps: [Copilot] for a repo
2. Have GitHub Copilot create a PR
3. DCO check fails despite config

Workaround

Currently using a GitHub Action to override the DCO status for Copilot PRs.

Additional Context

• Verified config is loaded via kubectl get configmap plugins -n prow -o yaml
• Verified commit author login matches Copilot via GitHub API
• Hook logs show DCO plugin running but no indication trusted_apps is being checked

/kind bug